This paper details the design for an industrial rainwater harvesting (RWH) system at the Linamar CAMTAC plant in Guelph. The purpose of the system is to substitute the use of city water in plant processes with rainwater. The design consists of three principal components: catchment, storage and treatment. The catchment is an internal drainage system that transmits rainwater from the roof to a storage tank. The tank reserves a rainwater supply for future demand. Treatment systems adjust rainwater parameters to the quality required for process water. Raw rainwater is subjected to first flow diversion, pH adjustment, filtration and ultraviolet (UV) disinfection before being processed by an existing reverse osmosis (RO) unit. The capital cost is projected to be approximately $18,500 with a payback period of 3.2 years.